The hearts of 53 patients (aged 61+ or -11 years, 34 men) who participated in the Thrombolysis in Myocardial Infarction Study (TIMI) and died from 5 hours to 260 days (median 2.6 days) after onset of chest pain were studied. Of the 53 patients, 38 received recombinant tissue plasminogen activator (rt-PA) without percutaneous transluminal coronary angioplasty (PTCA) (9 patients) or coronary artery bypass grafting (CABG) (6 patients). Comparisons between the 24 patients with hemorrhagic infarcts and the 20 patients with non-hemorrhagic infarcts showed: 1) similar frequencies of myocardial rupture (left ventricular free wall or ventricular septum) [6(25%) of 24 -vs- 5(25%) of 201, cardiogenic shock [9(41%) of 22 -vs- 7(44%) of 16), and fatal hemorrhage [2(10%) of 21 -vs- 3(19%) of 16]; 2) similar frequencies of thrombi in the infarct-related arteries [7(30% -vs- 7(37%)], but all thrombi in patients with hemorrhagic infarcts were non-occlusive, and all thrombi in those with non-hemorrhagic infarcts were occlusive (p=.0002);4) similar degrees of luminal narrowing (0-25%, 26-50%, 51-75%, 76-95%, 96-100%) in all 5-mm segments of the 4 major (left main, left anterior descending, left circumflex and right) epicardial coronary arteries in 27 patients receiving rt-PA alone; 5) similar mean percent reduction in cross-sectional area narrowing by plaque of the infarct-related arteries calculated by planimetry (67 + or -10% -vs- 68 + or -9%); 6) similar frequencies of plaque rupture [13(57%) - vs- 15(77%); p=.12]; 7) similar frequencies of hemorrhage into a plaque [(16(80%) -vs- 14(74%)]; 8) fewer right ventricular infarcts in patients with hemorrhagic infarcts [2 of 11 posterior hemorrhagic infarcts -vs- 6 of 9 posterior non-hemorrhagic infarcts; p=.031.9) similar percents of plaque with pultaceous debris (13 + or - 11% -vs- 18 + or - 9%; ,P=.18), calcific deposits (14 + or 12% -vs- 20 + or - 14%; p=.25), and acellular fibrous tissue (49 + or 14% -vs- 53 + or - 11%; p=.39).